NCP1250. Current-Mode PWM Controller for Off-line Power Supplies

Transcription

1 Current-Mode PWM Controller for Off-line Power Supplies The NCP50 is a highly integrated PWM controller capable of delivering a rugged and high performance offline power supply in a tiny TSOP 6 or PDIP 8 package. With a supply range up to 8 V, the controller hosts a jittered 65 khz or 00 khz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to a minimum level of 6 khz. As the power further goes down, the part enters skip cycle while limiting the peak current. Over Power Protection (OPP) is a difficult exercise especially when no load standby requirements drive the converter specifications. The ON proprietary integrated OPP lets you harness the maximum delivered power without affecting your standby performance simply via two external resistors. An Over Voltage Protection input is also combined on the same pin and protects the whole circuitry in case of optocoupler failure or adverse open loop operation. Finally, a timer based short circuit protection offers the best protection scheme, letting you precisely select the protection trip point irrespective of a loose coupling between the auxiliary and the power windings. Features Fixed Frequency 65 or 00 khz Current Mode Control Operation Internal and Adjustable Over Power Protection (OPP) Circuit Frequency Foldback Down to 6 khz and Skip Cycle in Light Load Conditions Internal Ramp Compensation Internal Fixed 4 ms Soft Start 00 ms Timer Based Auto Recovery Short Circuit Protection Frequency Jittering in Normal and Frequency Foldback Modes Option for Auto Recovery or Latched Short Circuit Protection OVP Input for Improved Robustness Up to 8 V V CC Operation +300 ma/ 500 ma Source/Sink Drive Capability Less than 00 mw Standby Power at High Line EPS.0 Compliant These are Pb Free Devices Typical Applications ac dc Converters for TVs, Set top Boxes and Printers Offline Adapters for Notebooks and Netbooks GND FB TSOP 6 (SOT3 6) SN SUFFIX CASE 38G PIN CONNECTIONS DRV OPP/Latch 3 4 CS TSOP 6 (Top View) 6 MARKING DIAGRAMS (Note: Microdot may be in either location) 5 V CC 5xAYW 5x = Specific Device Code x = A,, C, D, 0, y = A or B A = Assembly Location WL = Wafer Lot Y, YY = Year W, WW = Work Week G or = Pb Free Package GND DRV N/C V CC 3 PDIP 8 SUFFIX P Case PDIP 8 (Top View) 5xy65 AWL YYWWG OPP/LATCH N/C FB CS ORDERING INFORMATION See detailed ordering and shipping information in the package dimensions section on page 3 of this data sheet. Semiconductor Components Industries, LLC, 05 April, 05 Rev. 0 Publication Order Number: NCP50/D

2 Vbulk. Vout OVP. OPP. NCP ramp comp. Figure. Typical Application Example (TSOP 6) PIN DESCRIPTION PDIP 8 Pin N TSSOP 6 Pin Name Function Pin Description GND The controller ground. 6 FB Feedback pin Hooking an optocoupler collector to this pin will allow regulation. 8 3 OPP/OVP Adjust the Over Power Protection Latches off the part 5 4 CS Current sense + ramp compensation A resistive divider from the auxiliary winding to this pin sets the OPP compensation level. When brought above 3 V, the part is fully latched off. This pin monitors the primary peak current but also offers a means to introduce ramp compensation. 4 5 V CC Supplies the controller This pin is connected to an external auxiliary voltage and supplies the controller. 6 DRV Driver output The driver s output to an external MOSFET gate. OPTIONS Controller Frequency OCP Latched OCP Auto Recovery NCP50ASN65TG 65 khz Yes No NCP50BSN65TG 65 khz No Yes NCP50ASN00TG 00 khz Yes No NCP50BSN00TG 00 khz No Yes NCP50BP65G 65 khz No Yes

3 ORDERING INFORMATION Device Package Marking OCP Protection Switching Frequency Package Shipping NCP50ASN65TG 5A Latch 65 khz TSOP 6 (Pb Free) NCP50BSN65TG 5 Autorecovery 65 khz NCP50ASN00TG 5C Latch 00 khz NCP50BSN00TG 5D Autorecovery 00 khz NCP50BP65G 50B65 Autorecovery 65 khz PDIP 8 (Pb Free) 3000 / Tape & Reel 50 Units / Rail For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD80/D. OPP Vcc and logic management UVLO Vlatch OVP gone? 600 ns time constant Up counter RST 4 vdd power on reset hiccup IpFlag vdd S R Q Q us blanking Rlim Iscr Vcc Frequency modulation Power on reset khz clock Clamp S Q Q R Frequency foldback Drv Vfold Vskip vdd Rramp The soft start is activated during: 4 ms SS IpFlag RFB / 4. the startup sequence the auto recovery burst mode FB VFB <.05 V? setpoint = 50 mv CS LEB 50 mv peak current freeze VOPP + Vlimit + VOPP GND Vlimit Figure. Internal Circuit Architecture 3

4 MAXIMUM RATINGS TABLE Symbol Rating Value Unit V CC Power Supply voltage, V CC pin, continuous voltage 8 V V DRVtran Maximum DRV pin voltage when DRV in H state, transient voltage (Note ) V CC V Maximum voltage on low power pins CS, FB and OPP 0.3 to 0 V IOPP Maximum injected negative current into the OPP pin ma I SCR Maximum continuous current in to the V CC Pin while in latched mode 3 ma R JA Thermal Resistance Junction to Air 360 C/W T J,max Maximum Junction Temperature 50 C Storage Temperature Range 60 to +50 C ESD Capability, Human Body Model (HBM), all pins kv ESD Capability, Machine Model (MM) 00 V ESD Capability, Charged Device Model (CDM) kv Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected.. The transient voltage is a voltage spike injected to DRV pin being in high state. Maximum transient duration is 00 ns.. This device series contains ESD protection and exceeds the following tests: Human Body Model 000 V per JESD, Method A4E. Machine Model Method 00 V per JESD, Method A5A. Charged Device Model per JEDEC Standard JESD C0D 3. This device contains latch up protection and exceeds 00 ma per JEDEC Standard JESD78. 4

5 ELECTRICAL CHARACTERISTICS (For typical values T J = 5 C, for min/max values T J = 40 C to +5 C, Max T J = 50 C, V CC = V unless otherwise noted) Symbol Rating Min Typ Max Unit SUPPLY SECTION (For the best efficiency performance, we recommend a V CC below 0 V) VCC ON V CC increasing level at which driving pulses are authorized V VCC (min) V CC decreasing level at which driving pulses are stopped V VCC HYST Hysteresis VCC ON VCC (min) 6.0 V V ZENER Clamped V CC when latched off / burst mode I CC = 500 A 7.0 V ICC Start up current 5 A ICC Internal IC consumption with I FB = 50 A, F SW = 65 khz and C L = 0 nf.4. ma ICC3 Internal IC consumption with I FB = 50 A, F SW = 65 khz and C L = nf. 3.0 ma ICC Internal IC consumption with I FB = 50 A, F SW = 00 khz and C L = 0 nf.7.5 ma ICC3 Internal IC consumption with I FB = 50 A, F SW = 00 khz and C L = nf ma ICC LATCH Current flowing into V CC pin that keeps the controller latched (Note 4) T J = 40 C to +5 C T J = 0 C to +5 C ICCstby Internal IC consumption while in skip cycle (V CC = V, driving a typical 6 A/600 V MOS- FET) 40 3 A 550 A R lim Current limit resistor in series with the latch SCR 4.0 k DRIVE OUTPUT T r Output voltage rise C L = nf, 0 90% of output signal 40 ns T f Output voltage fall C L = nf, 0 90% of output signal 30 ns R OH Source resistance 3 R OL Sink resistance 6.0 I source Peak source current, V GS = 0 V (Note 5) 300 ma I sink Peak sink current, V GS = V (Note 5) 500 ma V DRVlow DRV pin level at V CC close to VCC (min) with a 33 k resistor to GND 8.0 V V DRVhigh DRV pin level at V CC = 8 V DRV unloaded 0 4 V CURRENT COMPARATOR I IB Input Bias 0.8 V input level on CS Pin 0.0 A V Limit Maximum internal current setpoint T J = 5 C OPP/Latch Pin grounded V V Limit Maximum internal current setpoint T J = 40 C to 5 C OPP/Latch Pin grounded V V fold Default internal voltage set point for frequency foldback trip point 45% of V limit 357 mv V freeze Internal peak current setpoint freeze ( 3% of V limit ) 50 mv T DEL Propagation delay from current detection to gate off state ns T LEB Leading Edge Blanking Duration 300 ns TSS Internal soft start duration activated upon startup, auto recovery 4.0 ms IOPPo Setpoint decrease for the OPP/Latch pin biased to 50 mv (Note 6) 3.3 % IOOPv Voltage setpoint for the OPP/Latch pin biased to 50 mv (Note 6), T J = 5 C V IOOPv Voltage setpoint for the OPP/Latch pin biased to 50 mv (Note 6), T J = 40 C to 5 C V IOPPs Setpoint decrease for the OPP/Latch pin grounded 0 % INTERNAL OSCILLATOR f OSC Oscillation frequency (65 khz version) khz f OSC Oscillation frequency (00 khz version) khz 5

6 ELECTRICAL CHARACTERISTICS (continued) (For typical values T J = 5 C, for min/max values T J = 40 C to +5 C, Max T J = 50 C, V CC = V unless otherwise noted) Symbol Rating INTERNAL OSCILLATOR D max Maximum duty cycle % f jitter Frequency jittering in percentage of f OSC ±5 % f swing Swing frequency 40 Hz FEEDBACK SECTION R up Internal pull up resistor 0 k R eq Equivalent ac resistor from FB to GND 6 k I ratio FB Pin to current setpoint division ratio 4. V freeze Feedback voltage below which the peak current is frozen.05 V FREQUENCY FOLDBACK V fold Frequency folback level on the feedback pin 45% of maximum peak current.5 V F trans Transition frequency below which skip cycle occurs 6 30 khz V fold,end End of frequency foldback feedback leve, F sw = F min 350 mv V skip Skip cycle level voltage on the feedback pin 300 mv Skip hysteresis Hysteresis on the skip comparator (Note 5) 30 mv INTERNAL SLOPE COMPENSATION V ramp Internal ramp 5 C (Note 7).5 V R ramp Internal ramp resistance to CS pin 0 k PROTECTIONS V latch Latching level input V T latch blank Blanking time after drive turn off.0 s T latch count Number of clock cycles before latch confirmation 4.0 T latch del OVP detection time constant 600 ns Timer Internal auto recovery fault timer duration ms Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. 4. For design robustness, we recommend to inject 60 A as a minimum at the lowest input line voltage. 5. Guaranteed by design 6. See characterization table for linearity over negative bias voltage 7. A M resistor is connected from OPP/Latch Pin to the ground for the measurement. Min Typ Max Unit 6

7 TYPICAL CHARACTERISTICS D max (%) F SW (khz) Figure Figure F trans (khz) F _swing (Hz) Figure 5. Figure 6. V limit (mv) Figure 7. V Lskip (mv) 490 F SW = 65 khz Figure 8. 7

8 TYPICAL CHARACTERISTICS IOOP O (%) 34 9 IOOP V (V) Figure Figure V CC(ON) (V) V CC(min) (V) Figure. Figure V CC(Hyst) (V) I CC ( A) Figure 3. Figure 4. 8

9 TYPICAL CHARACTERISTICS F SW = 65 khz.5 F SW = 65 khz.5 I CC (ma) I CC3 (ma) Figure 5. Figure V zener (V) I CCLatch ( A) Figure 7. Figure T leb (V) Req (k ) Figure 9. Figure 0. 9

10 TYPICAL CHARACTERISTICS Iratio ( ) V latch (V) Figure. Figure t rise (ns) t fall (ns) Figure 3. Figure R ol ( ) R oh ( ) Figure 5. Figure 6. 0

11 TYPICAL CHARACTERISTICS V ovp_del ( s) V drv_low (V) Figure 7. Figure 8. V drv_high (V) Figure 9. T SS (ms) Figure V fold(fb) (V) V fold(cs) (mv) Figure 3. Figure 3.

12 TYPICAL CHARACTERISTICS V fold_end (V) V skip (mv) Figure 33. Figure V freeze (mv) V freeze(fb) (V) Figure 35. Figure TIMER (ms) 30 0 I CC (ma) F SW = 65 khz Figure 37. ADAPTER OUTPUT CURRENT (A) Figure 38. Controller Consumption vs. Adapter Output Current

13 APPLICATION INFORMATION Introduction The NCP50 implements a standard current mode architecture where the switch off event is dictated by the peak current setpoint. This component represents the ideal candidate where low part count and cost effectiveness are the key parameters, particularly in low cost ac dc adapters, open frame power supplies etc. Capitalizing on the NCP0X series success, the NCP50 packs all the necessary components normally needed in today modern power supply designs, bringing several enhancements such as a non dissipative OPP. Current mode operation with internal ramp compensation: Implementing peak current mode control at a fixed 65 khz or 00 khz, the NCP50 offers an internal ramp compensation signal that can easily by summed with the sensed current. Sub harmonic oscillations are eliminated via the inclusion of a single resistor in series with the current sense information. Internal OPP: By routing a portion of the negative voltage present during the on time on the auxiliary winding to the dedicated OPP pin, the user has a simple and non dissipative means to alter the maximum peak current setpoint as the bulk voltage increases. If the pin is grounded, no OPP compensation occurs. If the pin receives a negative voltage down to 50 mv, then a peak current reduction down to 3.3% typical can be achieved. For an improved performance, the maximum voltage excursion on the sense resistor is limited to 0.8 V. Low startup current: Achieving a low no load standby power always represents a difficult exercise when the controller draws a significant amount of current during start up. Due to its proprietary architecture, the NCP50 is guaranteed to draw less than 5 A typical, easing the design of low standby power adapters. EMI jittering: An internal low frequency modulation signal varies the pace at which the oscillator frequency is modulated. This helps by spreading out energy in conducted noise analysis. To improve the EMI signature at low power levels, the jittering remains active in frequency foldback mode. Frequency foldback capability: A continuous flow of pulses is not compatible with no load/light load standby power requirements. To excel in this domain, the controller observes the feedback pin and when it reaches a level of.5 V, the oscillator then starts to reduce its switching frequency as the feedback level continues to decrease. When the feedback pin reaches.05 V, the peak current setpoint is internally frozen and the frequency continues to decrease. It can go down to 6 khz (typical) reached for a feedback level of roughly 350 mv. At this point, if the power continues to drop, the controller enters classical skip cycle mode. Internal soft start: A soft start precludes the main power switch from being stressed upon start up. In this controller, the soft start is internally fixed to 4 ms. The soft start is activated when a new startup sequence occurs or during an auto recovery hiccup. OVP input: The NCP50 includes a latch input Pin that can be used to sense an overvoltage condition on the adapter. If this pin is brought higher than the internal reference voltage V latch, then the circuit permanently latches off. The V CC pin is pulled down to a fixed level, keeping the controller latched. The latch reset occurs when the user disconnects the adapter from the mains and lets the V CC falls below the V CC reset. Short circuit protection: Short circuit and especially over load protections are difficult to implement for transformers with high leakage inductance between auxiliary and power windings (the aux winding level does not properly collapse in presence of an output short). Here, every time the internal 0.8 V maximum peak current limit is activated (or less when OPP is used), an error flag is asserted and a time period starts, thanks to an internal timer. If the timer reaches completion while the error flag is still present, the controller stops the pulses and goes into a latch off phase, operating in a low frequency burst mode. When the fault is cleared, the SMPS resumes operation. Please note that some versions offer an auto recovery mode as described and some latch off in case of a short circuit. Start up Sequence The NCP50 start up voltage is made purposely high to permit a large energy storage in a small V CC capacitor value. This helps to operate with a small start up current which, together with a small V CC capacitor, will not hamper the start up time. To further reduce the standby power, the start up current of the controller is extremely low, below 5 A maximum. The start up resistor can therefore be connected to the bulk capacitor or directly to the mains input voltage to further reduce the power dissipation. 3

14 3 R3 00k 0 R 00k D N D N4007 R 00k input mains Cbulk uf VCC D6 N448 D5 N D4 N4007 D3 N4007 C 4.7uF C3 47uF aux. Figure 39. The Startup Resistor Can Be Connected to the Input Mains for Further Power Dissipation Reduction The first step starts with the calculation of the V CC capacitor which will supply the controller when it operates until the auxiliary winding takes over. Experience shows that this time t can be between 5 ms and 0 ms. If we consider we need at least an energy reservoir for a t time of 0 ms, the V CC capacitor must be larger than: CV CC I CC t VCC on VCC min 3m 0m 3.3 F (eq. ) 9 Let us select a 4.7 F capacitor at first and experiments in the laboratory will let us know if we were too optimistic for the time t. The V CC capacitor being known, we can now evaluate the charging current we need to bring the V CC voltage from 0 to the VCC on of the IC, 8 V typical. This current has to be selected to ensure a start up at the lowest mains (85 V rms) to be less than 3 s (.5 s for design margin): VCC on C VCC I charge 34 A (eq. ).5.5 If we account for the 5 A that will flow inside the controller, then the total charging current delivered by the start up resistor must be 49 A. If we connect the start up network to the mains (half wave connection then), we know that the average current flowing into this start up resistor will be the smallest when V CC reaches the VCC on of the controller: V ac,rms VCC on I CVCC,min (eq. 3) R start up To make sure this current is always greater than 49 A, then the minimum value for R start up can be extracted: V ac,rms VCC on R start up I CVCC,min k (eq. 4) This calculation is purely theoretical, and assumes a constant charging current. In reality, the take over time can be shorter (or longer!) and it can lead to a reduction of the V CC capacitor. Hence, a decrease in charging current and an increase of the start up resistor, thus reducing the standby power. Laboratory experiments on the prototype are thus mandatory to fine tune the converter. If we chose the 43 k resistor as suggested by Equation 4, the dissipated power at high line amounts to: V ac,peak P Rstart up 4R start up k (eq. 5) mw 0.87Meg Now that the first V CC capacitor has been selected, we must ensure that the self supply does not disappear when in no load conditions. In this mode, the skip cycle can be so deep that refreshing pulses are likely to be widely spaced, inducing a large ripple on the V CC capacitor. If this ripple is too large, chances exist to touch the VCC min and reset the controller into a new start up sequence. A solution is to grow this capacitor but it will obviously be detrimental to the start up time. The option offered in Figure 39 elegantly solves this potential issue by adding an extra capacitor on the auxiliary winding. However, this component is separated from the V CC pin via a simple diode. You therefore have the ability to grow this capacitor as you need to ensure the self supply of the controller without jeopardizing the start up time and standby power. A capacitor ranging from to 47 F is the typical value for this device. One note on the start-up current. If reducing it helps to improve the standby power, its value cannot fall below a certain level at the minimum input voltage. Failure to inject 4

15 enough current (30 A) at low line will turn a converter in fault into an auto-recovery mode since the SCR won t remain latched. To build a sufficient design margin, we recommend to keep at least 60 A flowing at the lowest input line (80 V rms for 85 V minimum for instance). An excellent solution is to actually combine X discharge and start-up networks as proposed in Figure 3 of application note AND8488/D. Internal Over Power Protection There are several known ways to implement Over Power Protection (OPP), all suffering from particular problems. These problems range from the added consumption burden on the converter or the skip cycle disturbance brought by the current sense offset. A way to reduce the power capability at high line is to capitalize on the negative voltage swing present on the auxiliary diode anode. During the power switch on time, this point dips to NV in, N being the turns ratio between the primary winding and the auxiliary winding. The negative plateau observed on Figure 4 will have an amplitude dependant on the input voltage. The idea implemented in this chip is to sum a portion of this negative swing with the 0.8 V internal reference level. For instance, if the voltage swings down to 50 mv during the on time, then the internal peak current set point will be fixed to = 650 mv. The adopted principle appears in Figure 4 and shows how the final peak current set point is constructed. v(4) 40.0 off time 0.0 N (V out +V f ) v(4) (V) N V bulk 40.0 on time 464u 47u 480u 488u 496u time (s) Figure 40. The Signal Obtained on the Auxiliary Winding Swings Negative During the On time Let s assume we need to reduce the peak current from.5 A at low line, to A at high line. This corresponds to a 0% reduction or a set point voltage of 640 mv. To reach this level, then the negative voltage developed on the OPP pin must reach: V OPP 640m 800m 60 mv (eq. 6) 5

16 RoppU VCC aux swings to: Vout during toff N V in during ton This p oin t will be adjusted to reduce the ref at hi line to the desired level. VDD from FB reset Iopp R oppl OPP K SU M ref K 0.8 V 5% ref = 0.8 V + VOPP CS + (V O P P is negativ e) Figure 4. The OPP Circuitry Affects the Maximum Peak Current Set Point by Summing a Negative Voltage to the Internal Voltage Reference Let us assume that we have the following converter characteristics: V out = 9 V V in = 85 to 65 V rms N = N p :N s = :0.5 N = N p :N aux = :0.8 Given the turns ratio between the primary and the auxiliary windings, the on time voltage at high line (65 Vac) on the auxiliary winding swings down to: V aux N V in,max V (eq. 7) To obtain a level as imposed by Equation 6, we need to install a divider featuring the following ratio: Div 0.6.4m (eq. 8) 67.5 If we arbitrarily fix the pull down resistor R OPPL to k, then the upper resistor can be obtained by: R OPPU 4 k (eq. 9) 0.6 k If we now plot the peak current set point obtained by implementing the recommended resistor values, we obtain the following curve (Figure 4): Peak current setpoint 00% 80% 375 V bulk Figure 4. The Peak Current Regularly Reduces Down to 0% at 375 Vdc The OPP pin is surrounded by Zener diodes stacked to protect the pin against ESD pulses. These diodes accept some peak current in the avalanche mode and are designed to sustain a certain amount of energy. On the other side, negative injection into these diodes (or forward bias) can cause substrate injection which can lead to an erratic circuit behavior. To avoid this problem, the pin is internally clamped slightly below 300 mv which means that if more current is injected before reaching the ESD forward drop, then the maximum peak reduction is kept to 40%. If the voltage finally forward biases the internal zener diode, then care must be taken to avoid injecting a current beyond ma. Given the value of R OPPU, there is no risk in the present example. 6

17 Finally, please note that another comparator internally fixes the maximum peak current set point to 0.8 V even if the OPP pin is inadvertently biased above 0 V. Frequency Foldback The reduction of no load standby power associated with the need for improving the efficiency, requires a change to the traditional fixed frequency type of operation. This controller implements a switching frequency foldback when the feedback voltage passes below a certain level, V fold, set around.5 V. At this point, the oscillator enters frequency Frequency foldback and reduces its switching frequency. The peak current setpoint follows the feedback pin until its level reaches.05 V. Below this value, the peak current freezes to V fold /4. (50 mv or 3% of the maximum 0.8 V setpoint) and the only way to further reduce the transmitted power is to reduce the operating frequency down to 6 khz. This value is reached at a voltage feedback level of 350 mv typically. Below this point, if the output power continues to decrease, the part enters skip cycle for the best noise free performance in no load conditions. Figure 43 depicts the adopted scheme for the part. Peak current setpoint FB 65 khz F sw max 0.8 V V CS max 6 khz min 0.36 V 0.5 V min V FB V FB 350 mv.5 V 3.4 V V freeze V fold 3.4 V V fold,end Vfold.05 V.5 V Figure 43. By Observing the Voltage on the Feedback Pin, the Controller Reduces its Switching Frequency for an Improved Performance at Light Load Auto Recovery Short Circuit Protection In case of output short circuit or if the power supply experiences a severe overloading situation, an internal error flag is raised and starts a countdown timer. If the flag is asserted longer than 00 ms, the driving pulses are stopped and the V CC pin slowly goes down to around 7 V. At this point, the controller wakes up and the V CC builds up again due to the resistive starting network. When V CC reaches VCC ON, the controller attempts to re start, checking for the absence of the fault. If the fault is still there, the supply enters another cycle of so called hiccup mode. If the fault has cleared, the power supply resumes normal operation. Please note that the soft start is activated during each of the re start sequence. 7

18 vcc vdrv 3 ilprim V cc (t) Plot vdrv in volts 6.05 vcc in volts 3.89 ilprim in amperes.38 V DRV (t).7..4 SS I Lp (t) m 3 500u.50m.50m 3.50m 4.50m time in seconds Figure 44. An Auto Recovery Hiccup Mode is Activated for Faults Longer than 00 ms Slope Compensation The NCP50 includes an internal ramp compensation signal. This is the buffered oscillator clock delivered only during the on time. Its amplitude is around.5 V at the maximum duty cycle. Ramp compensation is a known means used to cure sub harmonic oscillations in Continuous Conduction Mode (CCM) operated current mode converters. These oscillations take place at half the switching frequency and occur only during CCM with a duty cycle greater than 50%. To lower the current loop gain, one usually injects between 50% and 00% of the inductor downslope. Figure 45 depicts how internally the ramp is generated. Please note that the ramp signal will be disconnected from the CS pin, during the off time..5 V 0V ON latch reset 0k Rcomp + LEB CS Rsense from FB setpoint Figure 45. Inserting a Resistor in Series with the Current Sense Information Brings Ramp Compensation and Stabilizes the Converter in CCM Operation. In the NCP50 controller, the oscillator ramp features a.5 V swing reached at a 80% duty ratio. If the clock operates at a 65 khz frequency, then the available oscillator slope corresponds to: S ramp V ramp,peak D max T SW (eq. 0) 08 kv s or08mv s 8

19 In our flyback design, let s assume that our primary inductance L p is 770 H, and the SMPS delivers 9 V with a N p :N s ratio of :0.5. The off time primary current slope S p is thus given by: S p Vout V f N p N s L p (9 0.8) ka s (eq. ) Given a sense resistor of 330 m, the above current ramp turns into a voltage ramp of the following amplitude: S sense S p R sense 03k 0.33 (eq. ) 34 kv s or34mv s If we select 50% of the downslope as the required amount of ramp compensation, then we shall inject a ramp whose slope is 7 mv/ s. Our internal compensation being of 08 mv/ s, the divider ratio (divratio) between R comp and the internal 0 k resistor is: divratio 7m 0.08 (eq. 3) 08m The series compensation resistor value is thus: R comp R ramp divratio 0k k (eq. 4) A resistor of the above value will then be inserted from the sense resistor to the current sense pin. We recommend adding a small capacitor of 00 pf, from the current sense pin to the controller ground for an improved immunity to the noise. Please make sure both components are located very close to the controller. Latching Off the Controller The OPP pin not only allows a reduction of the peak current set point in relationship to the line voltage, it also offers a means to permanently latch off the part. When the part is latched off, the V CC pin is internally pulled down to around 7 V and the part stays in this state until the user cycles the V CC down and up again, e.g. by un plugging the converter from the mains outlet. It is important to note that the SCR maintains its latched state as long as the injected current stays above the minimum value of 30 A. As the SCR delatches for an injected current below this value, it is the designer duty to make sure the injected current is high enough at the lowest input voltage. Failure to maintain a sufficiently high current would make the device auto recover. A good design practice is to ensure at least 60 A at the lowest input voltage. The latch detection is made by observing the OPP pin by a comparator featuring a 3 V reference voltage. However, for noise reasons and in particular to avoid the leakage inductance contribution at turn off, a s blanking delay is introduced before the output of the OVP comparator is checked. Then, the OVP comparator output is validated only if its high state duration lasts a minimum of 600 ns. Below this value, the event is ignored. Then, a counter ensures that 4 successive OVP events have occurred before actually latching the part. There are several possible implementations, depending on the needed precision and the parameters you want to control. The first and easiest solution is the additional resistive divider on top of the OPP one. This solution is simple and inexpensive but requires the insertion of a diode to prevent disturbing the OPP divider during the on time. R3 5k D N448 RoppU 4k 0 OP P 4 VCC 9 8 aux. winding C 00p ROPPL k Vlatch 5 OVP OPP Figure 46. A Simple Resistive Divider Brings the OPP Pin Above 3 V in Case of a V CC Voltage Runaway above 8 V First, calculate the OPP network with the above equations. Then, suppose we want to latch off our controller when V out exceeds 5 V. On the auxiliary winding, the plateau reflects the output voltage by the turns ratio between the power and the auxiliary winding. In case of voltage runaway for our 9 V adapter, the plateau will go up to: V aux,ovp V (eq. 5) Since our OVP comparator trips at a 3 V level, across the k selected OPP pulldown resistor, it implies a 3 ma current. From 3 V to go up to 8 V, we need an additional 9

20 5 V. Under 3 ma and neglecting the series diode forward drop, it requires a series resistor of: R OVP V latch V VOP V OVP R OPPL k 5 5k (eq. 6) 3m In nominal conditions, the plateau establishes to around 4 V. Given the divide by 6 ratio, the OPP pin will swing to 4/6 =.3 V during normal conditions, leaving 700 mv margin. A 00 pf capacitor can be added between the OPP pin and GND to improve noise immunity and avoid erratic trips in presence of external surges. Do not increase this capacitor too much otherwise the OPP signal will be affected by the integrating time constant. A second solution for the OVP detection alone, is to use a Zener diode wired as recommended by. D3 5V D N448 ROPPU 4k 0 OPP 4 VCC 9 8 aux. winding C pf ROPPL k Vlatch 5 OVP OPP Figure 47. A Zener Diode in Series with a Diode Helps to Improve the Noise Immunity of the System For this configuration to maintain an 8 V level, we have selected a 5 V Zener diode. In nominal conditions, the voltage on the OPP pin is almost 0 V during the off time as the Zener is fully blocked. This technique clearly improves the noise immunity of the system compared to that obtained from a resistive string as in Figure 46. Please note the reduction of the capacitor on the OPP pin to 0 pf pf. This capacitor is necessary because of the potential spike coupling through the Zener parasitic capacitance from the bias winding due to the leakage inductance. Despite the s blanking delay at turn off. This spike is energetic enough to charge the added capacitor C and given the time constant, could make it discharge slower, potentially disturbing the blanking circuit. When implementing the Zener option, it is important to carefully observe the OPP pin voltage (short probe connections!) and check that enough margin exists to that respect. Over Temperature Protection In a lot of designs, the adapter must be protected against thermal runaways, e.g. when the temperature inside the adapter box increases above a certain value. Figure 48 shows how to implement a simple OTP using an external NTC and a series diode. The principle remains the same: make sure the OPP network is not affected by the additional NTC hence the presence of this isolation diode. When the NTC resistance decreases as the temperature increases, the voltage on the OPP pin during the off time will slowly increase and, once it passes 3 V for 4 consecutive clock cycles, the controller will permanently latch off. 0

21 NT C D N448 ROPPU 84k VCC OP P au x. winding ROPPL.5k Vlatch full latch OPP Figure 48. The Internal Circuitry Hooked to OPP/Latch Pin Can Be Used to Implement Over Temperature Protection (OTP) Back to our 9 V adapter, we have found that the plateau voltage on the auxiliary diode was 3 V in nominal conditions. We have selected an NTC which offers a resistance of 470 k at 5 C and drops to 8.8 k at 0 C. If our auxiliary winding plateau is 4 V and we consider a 0.6 V forward drop for the diode, then the voltage across the NTC in fault mode must be: V NTC V (eq. 7) Based on the 8.8 k NTC resistor at 0 C, the current through the device must be: I NTC 0.4. ma (eq. 8) 8.8k As such, the bottom resistor R OPPL, can easily be calculated: R OPPL 3.5 k (eq. 9).m Now that the pulldown OPP resistor is known, we can calculate the upper resistor value R OPPU to adjust the power limit at the chosen output power level. Suppose we need a 00 mv decrease from the 0.8 V set point and the on time swing on the auxiliary anode is 67.5 V, then we need to drop over R OPPU a voltage of: V ROPPU V (eq. 0) The current flowing in the pulldown resistor R OPPL in this condition will be: I ROPPU 00m 80 A (eq. ).5k The R OPPU value is therefore easily derived: R OPPU k (eq. ) 80 Combining OVP and OTP The OTP and Zener based OVP can be combined together as illustrated by Figure 49.

22 D3 5V NT C D N448 ROPPU 84k OPP VCC 9 8 au x. winding 0 4 ROPPL.5k 5 Vlatch OVP OPP Figure 49. With the NTC Back in Place, the Circuit Nicely Combines OVP, OTP and OPP on the Same Pin In nominal V CC / output conditions, when the Zener is not activated, the NTC can drive the OPP pin and trigger the adapter in case of an over temperature. During nominal temperature if the loop is broken, the voltage runaway will be detected and the controller will shut down the converter. In case the OPP pin is not used for either OPP or OVP, it can simply be grounded. Zener diode and the series diode. To prevent an adverse triggering of the Over Voltage Protection circuitry, it is possible to install a small RC filter before the detection network. Typical values are those given in Figure 50 and must be selected to provide the adequate filtering function without degrading the stand by power by an excessive current circulation. Filtering the Spikes The auxiliary winding is the seat of spikes that can couple to the OPP pin via the parasitic capacitances exhibited by the D3 5V ad d ition al fil ter NT C D N448 ROPPU 84k C 330pF R3 0 OP P VCC 9 3 aux. winding 0 4 ROPPL.5k 5 Vlatch OVP OPP Figure 50. A Small RC Filter Avoids the Fast Rising Spikes from Reaching the Protection Pin of the NCP50 in Presence of Energetic Perturbations Superimposed on the Input Line

23 PACKAGE DIMENSIONS TSOP 6 CASE 38G 0 ISSUE V E NOTE 5 e 0.05 A D ÉÉÉ 3 b E A c L H M DETAIL Z DETAIL Z L GAUGE PLANE C SEATING PLANE NOTES:. DIMENSIONING AND TOLERANCING PER ASME Y4.5M, CONTROLLING DIMENSION: MILLIMETERS. 3. MAXIMUM LEAD THICKNESS INCLUDES LEAD FINISH. MINIMUM LEAD THICKNESS IS THE MINIMUM THICKNESS OF BASE MATERIAL. 4. DIMENSIONS D AND E DO NOT INCLUDE MOLD FLASH, PROTRUSIONS, OR GATE BURRS. MOLD FLASH, PROTRUSIONS, OR GATE BURRS SHALL NOT EXCEED 0.5 PER SIDE. DIMENSIONS D AND E ARE DETERMINED AT DATUM H. 5. PIN ONE INDICATOR MUST BE LOCATED IN THE INDICATED ZONE. MILLIMETERS DIM MIN NOM MAX A A b c D E E e L L 0.5 BSC M RECOMMENDED SOLDERING FOOTPRINT* 6X X PITCH DIMENSIONS: MILLIMETERS *For additional information on our Pb Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. 3

24 PACKAGE DIMENSIONS NOTE 8 A D D b TOP VIEW e/ e SIDE VIEW A E B A A NOTE 3 L C SEATING PLANE H PDIP 8 CASE ISSUE N eb 8X b END VIEW 0.00 M C A M B M NOTE 6 E c END VIEW WITH LEADS CONSTRAINED M NOTE 5 NOTES:. DIMENSIONING AND TOLERANCING PER ASME Y4.5M, CONTROLLING DIMENSION: INCHES. 3. DIMENSIONS A, A AND L ARE MEASURED WITH THE PACK- AGE SEATED IN JEDEC SEATING PLANE GAUGE GS DIMENSIONS D, D AND E DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS ARE NOT TO EXCEED 0.0 INCH. 5. DIMENSION E IS MEASURED AT A POINT 0.05 BELOW DATUM PLANE H WITH THE LEADS CONSTRAINED PERPENDICULAR TO DATUM C. 6. DIMENSION E3 IS MEASURED AT THE LEAD TIPS WITH THE LEADS UNCONSTRAINED. 7. DATUM PLANE H IS COINCIDENT WITH THE BOTTOM OF THE LEADS, WHERE THE LEADS EXIT THE BODY. 8. PACKAGE CONTOUR IS OPTIONAL (ROUNDED OR SQUARE CORNERS). INCHES MILLIMETERS DIM MIN MAX MIN MAX A A A b b TYP.5 TYP C D D E E e 0.00 BSC.54 BSC eb L M 0 0 ON Semiconductor and the are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries. SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC s product/patent coverage may be accessed at /site/pdf/patent Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Typical parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typicals must be validated for each customer application by customer s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 563, Denver, Colorado 807 USA Phone: or Toll Free USA/Canada Fax: or Toll Free USA/Canada orderlit@onsemi.com N. American Technical Support: Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: Japan Customer Focus Center Phone: ON Semiconductor Website: Order Literature: For additional information, please contact your local Sales Representative NCP50/D